Stuart Hutter

Advisor: Tilahun Adera, MPH, PhD

Preceptor: Robert Suruki, ScD

Introduction: Asthma is a common debilitating disease of the airways that afflicts an estimated 300 million worldwide, causing reduction in physical activity, lost school/work days, and even death.  There are many known and suspected risk factors of asthma; however, there is much controversy over prior and current cigarette smoking.  Approximately 25% of the United States population currently smokes, with a quarter of these being asthma patients.  Another 22 to 43 percent of asthmatics are ex-smokers.
 
Objectives: (1) To estimate the prevalence for lifetime asthma in the adult US population; (2) to determine prevalence odds ratios (POR) of lifetime asthma based on questionnaire (smoking status, tobacco consumption) after adjustment of potential confounding variables; (3) to determine POR of lifetime asthma based on laboratory values (serum cotinine); and (4) to assess the validity of self-reported measures (smoking status and tobacco consumption) using serum cotinine as the gold standard.

Methods: The National Health and Nutrition Examination Survey (NHANES) 1999-2002 is a proportional cross-sectional sample that uses weights to be representative.  Crude odds ratios were obtained through univariate analysis; multiple logistic regression analysis was used to obtain adjusted odds ratios of asthma.  Interactions for age, gender, and race/ethnicity were explored.  Validity measures included sensitivity and specificity tests for self-reported smoking and non-parametric correlation of tobacco consumption with serum cotinine levels.

Results: The overall prevalence of lifetime asthma among n=10,252 adults was 11.56% (95%CI 10.45-12.66).  Analyses were stratified by race/ethnicity due to significant interaction.  After adjusting for age, gender, body mass index, and family history of asthma, ex-smoking non-Hispanic Whites, non-Hispanic Blacks, and other races had odds ratios of 1.57 (95%CI 1.26-1.97), 1.52 (95%CI 1.01-2.27), and 1.97 (95%CI 1.01-3.83), respectively, relative to never smokers within their respective race/ethnic groups.  Sample persons with a family history of asthma and increasing body mass index were significant predictors for lifetime asthma among all race/ethnic groups.  Based on laboratory values, non-Hispanic White respondents with serum cotinine levels of 0.011 to <15ng/ml and ≥15ng/ml were 61% (9-138%) and 38% (4-83%), respectively, more likely to have lifetime asthma relative to non-Hispanic Whites with undetectable levels.  No dose-dependent relationship is evident.  Self-reported smoking showed 92% sensitivity and 94% specificity with a positive predictive value of 88%.  The overall smoker misclassification rate was 2.45%.  Daily tobacco consumption was significantly correlated with serum cotinine in the total population (r=0.532, p < 0.0001).
    
Discussion: Self-reported smoking and tobacco consumption are valid measures of tobacco use.  The present study found no significant relationship between current smoking and lifetime asthma. Despite the limited findings, asthmatic smokers make up a distinct, difficult-to-treat subgroup for which future treatment research should address.